This invention applies to methods and compositions for the removal of mercury species from crude oil streams, hydrocarbons, and/or gas condensates using dithiocarbamates with or without electrostatic coalescence. In many forms of crude oil a variety of mercury-containing species are present. These include but may not be limited to elemental mercury, mercuric chloride, mercuric, sulfide, mercuric selenide, and various combinations thereof. Also the mercury can be a chemical component of a variety of asphaltic and sulfur containing complexes and compounds. As an example, crude oils from the Austral Basin region of Argentina frequently contain well over 2000 ppb of mercury. Changes in the economics of the oil industry have resulted in such mercury bearing crude oils to be more commonly used.
It is important that these mercury-containing species be removed from the crude oil as they pose significant product quality and environmental and safety issues. As volatile compounds, the presence of mercury-containing species make processing and handling of the crude oil hazardous and unpredictable. Because the species are often toxic they render whatever hydrocarbons they end up in either unsafe to handle or beyond various established safety, pollution, and/or legal standards. Also the species tend to have unwanted side reactions with various additives used in the refining process or used to enhance the performance of the final hydrocarbon product. For example mercury species are known to destroy hydrotreating and other catalysts used to make the oil refining process economical.
Mercury bearing species are particularly odious to naphtha. In the crude oil refining process, naphtha is produced as a fraction of a distillation step. Mercury bearing species congregate within this fraction resulting in naphtha that is concentrated with unwanted mercury. This greatly reduces the value and use of this naphtha.
Currently, adsorbents, gas stripping, and chemical precipitation methods are being used to remove mercury from crudes and other hydrocarbon liquids prior to their processing in order to avoid catalyst poisoning problems. The use of fixed bed adsorbents, such as 30 activated carbon, molecular sieves, metal oxide-based adsorbents and activated alumina, to remove the mercury is a potentially simple approach but has several disadvantages. For example, solids in the crude oil tend to plug the adsorbent bed, and the cost of the adsorbent may be excessive when mercury levels are greater than 100 to 300 ppb. Also, large quantities of spent adsorbent are produced when treating hydrocarbon liquids having high levels of mercury, thereby making it imperative to process the spent adsorbent to remove adsorbed mercury before either recycle or disposal of the adsorbent.
Gas stripping also has drawbacks. To be effective the stripping must be conducted at high temperature with relatively large amounts of stripping gas. Since crudes contain a substantial amount of light hydrocarbons that are stripped with the mercury, these hydrocarbons must be condensed and recovered to avoid substantial product loss. Moreover, the stripping gas must either be disposed of or recycled, both of which options require the stripped mercury to be removed from the stripping gas.
Chemical precipitation includes the use of sodium sulfide or other sulfur-containing compounds to convert mercury in the liquid hydrocarbons into solid mercury sulfide, which is then separated from the hydrocarbon liquids through filtration (U.S. Pat. No. 6,537,443). As taught in the prior art, this method requires significant volumes of aqueous sodium sulfide solutions to be mixed with the liquid hydrocarbons. The drawbacks of this requirement include the necessity to maintain significant volumes of two liquid phases in an agitated state to promote contact between the aqueous sodium sulfide solution and the hydrocarbon liquids, which in turn can lead to the formation of an oil-water emulsion that is difficult to separate.
U.S. Pat. Nos. 6,537,443 and 6,685,824 documents the use of polymeric dithiocarbamate, monomeric dithiocarbamates, sulfurized olefins, and diatomaceous earth or zeolites impregnated with sulfur bearing compounds to remove mercury bearing species. They add the sulfur-containing compounds to the hydrocarbon to form a solid sulfur-mercury complex that requires removal using a hydrocarbon—water separation step following filtration of the hydrocarbon. U.S. Pat. Nos. 7,341,667, 7,449,118, and 7,479,230 describe the use of used alumina to reduce the level of inorganic contaminants, such as mercury and arsenic, from waste fluid streams. The alumina in this process is used Claus catalyst, which is used to recover elemental sulfur from hydrogen sulfide in gases. The waste fluid streams are passed through a filter containing the used Claus catalyst removing both elemental and ionic mercury. U.S. Pat. No. 7,476,3659 discloses a method and apparatus to remove elemental mercury from natural gas by condensing the mercury and gas via a cooler. The elemental mercury is collected the bottom of the vessel. None of these methods however allow for the mercury removal processes to occur with an in situ method using commonly available oilfield water/oil separation equipment or refinery water/oil equipment. As a result because they require additional cumbersome steps with more costly equipment they are unsatisfactory solutions to the problem. Thus there is clear utility in compositions, methods, and apparatuses that remove mercury species from crude oil streams, hydrocarbons, and/or gas condensates.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.